1. Field of the Invention
The present invention relates in general to an actuator and an ink jet print head including the actuator, and more particularly to an actuator which exhibits improved operating characteristics with high stability, and an ink jet print head using such an actuator as an ink pump for discharging an ink material from the print head.
2. Discussion of the Related Art
As a means for raising a pressure in a pressure chamber formed within a substrate of an actuator, there is recently known a piezoelectric/electrostrictive element formed on a wall defining the pressure chamber, for changing a volume of the pressure chamber due to displacement of the piezoelectric/electrostrictive element. Such an actuator may be used as an ink pump or the like of a print head used in an ink jet printer, for example. The actuator used as the ink pump is adapted to raise a pressure in the pressure chamber which is filled with an ink material, utilizing the displacement of the piezoelectric/electrostrictive element, so that fine ink particles are jetted or discharged through a nozzle that communicates with the pressure chamber, so as to effect printing by the print head.
Referring to FIGS. 4 and 5 showing a known example of the ink jet print head as described above, a metallic nozzle plate 4 having a plurality of nozzles 2, a metallic orifice plate 8 having a plurality of orifices 6, and a channel plate 10 are superposed on each other such that the channel plate 10 is interposed between the plates 4, 8, and these plates 4, 8, 10 are bonded together into an ink nozzle member 16. In this ink nozzle member 16, there are formed a plurality of ink discharge channels 12 for leading or guiding an ink material to the respective nozzles 2, and at least one ink supply channel 14 for leading or supplying the ink material to the orifices 6. Reference numeral 25 denotes an actuator which includes a substrate 24 consisting of a closure plate 18 and a spacer plate 20 both made of a metal or synthetic resin, and a plurality of piezoelectric/electrostrictive elements 28 formed on an outer surface of the closure plate 18. The closure plate 18 and spacer plate 20 are superposed on each other and formed integrally into the substrate 24, such that a plurality of voids 22 which correspond to the nozzles 2 and orifices 6 of the ink nozzle member 16 are formed in the substrate 24. The piezoelectric/electrostrictive elements 28 fixed to the closure plate 18 are aligned with the voids 22 of the substrate 24, as viewed in the plane of the substrate 24 (perpendicular to the direction of the thickness of the substrate 24). With the ink nozzle member 16 and the actuator 25 superposed on each other and bonded together by a suitable adhesive 29, each of the voids 22 provides a pressure chamber 26 formed behind the corresponding nozzle and orifice 2, 6 and filled with the ink material. In operation, the piezoelectric/electrostrictive elements 28 are selectively actuated to deform walls defining the corresponding pressure chamber or chambers 26, as schematically shown in FIG. 6, so as to change the pressure of the selected pressure chamber(s) 26.
In the ink jet print head as described above, the ink nozzle member 16 is bonded to the actuator 25, more precisely, to the surface of the spacer plate 20 on which the voids 22 are open. In this arrangement, a fluid-tight seal between the ink nozzle member 16 and the actuator 25 must be secured over a relatively large area surrounding the voids 22. Upon mass production of print heads of the above type, therefore, it is difficult for the print heads to assure a high degree of sealing reliability or fluid tightness and desired ink-jetting capability with high stability.
In view of the above problems, an actuator 40 as schematically shown in FIG. 7a has been proposed by the present inventors in co-pending U.S. patent application Ser. Nos. 08/066,193 and 08/066,195. This actuator 40 includes a ceramic substrate 38 having a plurality of pressure chambers 36 formed therein, and a plurality of film-like piezoelectric/electrostrictive elements 33 formed on the substrate 38. More specifically, ceramic green sheets for a spacer plate 30, a closure plate 32 and a connecting plate 34 are laminated on each other and co-fired into the ceramic substrate 38, such that the closure plate 32 is superposed on one surface of the spacer plate 30, and the connecting plate 34 having through-holes 35 is superposed on the other surface of the spacer plate 30. The piezoelectric/electrostrictive elements 33 are formed on the outer surface of the closure plate 32 by a film forming methods. When this actuator 40 is bonded to an ink nozzle member 42 by an adhesive 46, such that the communication holes 35 of the connecting plate 34 are aligned with nozzles 44 formed through the ink nozzle member 42, a fluid-tight seal needs to be provided only over a relatively small area surrounding the through-holes 35, readily assuring improved sealing reliability upon mass production of the print heads.
However, a further study by the inventors on the actuator 40 as described above revealed that the pressure chambers 36 are substantially entirely defined or surrounded by the integral ceramic substrate 38, whereby the ceramic substrate 38 is less likely to be deformed or displaced to change the pressure of the pressure chambers 36, due to increased rigidity of the substrate 38, as shown in FIG. 7b. Consequently, the operating characteristics of the actuator 40 may deteriorate, and the ink jet print head using the actuator 40 as an ink pump may not be able to provide desired ink-jetting capability.